1. Field of the Invention
The present invention relates generally to a method of producing gas from gas hydrates. More specifically, the invention is a method for contacting a gas hydrate formation with warmer water from an aquifer to release sequestered gas.
2. Description of the Prior Art
A gas hydrate is a crystalline solid that consists of a gas molecule surrounded by water molecules. The structure is similar to ice, except that the crystalline structure is stabilized by the presence of the gas molecule. The two molecules are dissimilar, but mechanically intermingled, without true chemical bonding. Gas hydrates may be formed of a number of gasses having an appropriate molecular size. These include carbon dioxide, hydrogen sulfide and several low-carbon-number hydrocarbons, including methane. Natural gas hydrates are modified ice structures enclosing methane and possibly other hydrocarbons.
Hydrates tend to form in the pore spaces of sediment layers. However they may also be seen as nodules or deposits of pure hydrate. Gas hydrates are stable at the temperature and pressures typically found on the ocean floor at depths greater than about 500 m. This depth may vary depending on the conditions of a specific location, for instance, hydrates do not tend to form until a depth of approximately 800 m in the eastern United States. Gas hydrates may also be stable in association with permafrost, both on- and off-shore. Natural gas hydrates act as a gas concentrator in that one unit volume of hydrate is equivalent to about 172 unit volumes of methane gas at standard conditions. Often however, the hydrate itself is dilute in the sediment, occupying 2% of the volume on average.
Methane gas trapped in hydrates represent a huge potential source for cleaner energy. One of the key problems in exploiting these hydrate deposits involves finding appropriate methods to produce and collect the gas. This invention describes a production system that creates an appropriate completion to tap heat from an underlying aquifer and efficiently release the gas from the hydrate deposit to produce it to surface. In addition, it is proposed to sequester CO2 in the form of hydrate at the same location following the methane extraction. This process, not only serves to sequester CO2 and help the environment, but could also be used to stabilize the sea bed following methane extraction.